An optical thread breakage monitoring apparatus for tufting machines contains a laser (36), a mirror wheel (17) which is illuminated by the laser and also a plurality of spaced apart strip-like deflecting mirrors (23, 11, 12) which direct the laser light which is cyclically deflected by the mirror wheel (17) onto a horizontally disposed concave mirror (13) which is arranged above the mirror wheel (17) and the deflecting mirrors (11, 12) and which forms the scanning beam (20'") which is directed towards the row of needles (14) of the tufting machine. A retroreflecting strip (15) is arranged behind the row of needles (14). The receipt of the light reflected from the retroreflecting strip (15) takes place in autocollimation (FIG. 1).